Park workers called in the Environment Agency and government department Defra after making grim discovery.

A spokesman for the Animal Health and Veterinary Laboratories Agency, which is carrying out the tests on behalf of Defra, said: “Investigations are taking place under the Wildlife Incidents Investigation Scheme and there should be no cause for public concern.”

Canadian Geese, Mallards, Coots and Tufted Ducks are among the species that reside in the lake, which is overlooked by a community cafe.

Signs were placed around the Manchester council-owned park warning visitors to steer clear of the water and linking the deaths to possible contamination by poisonous algae.

The signs state: “WARNING: the water has been contaminated with toxic algae which is harmful to health. Do not drink the water, swim, or allow pets in the water. Avoid contact with the algae.”

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Council officials sounded a note of caution and said it was still too early to determine the exact cause of the birds’ deaths.

Volunteers from the King William fishing club have been helping park officials remove the animals from the scene.

A spokesman for Manchester Council said: "This is a very distressing situation and we have been working closely with volunteers from the King William fishing club, who regularly use the lake at Boggart Hole Clough and have been helping us remove dead birds from the water as quickly as possible.

"Defra have carried out an autopsy on one of the birds, and the Environment Agency have visited the site to take water samples. We are currently waiting for the results of both tests. However, as a precaution we are asking park visitors not to enter the water or allow pet dogs to do so.

"We have put aerators in the lake as a temporary measure to alleviate this problem and have recently approved plans which will permanently improve the lake's water quality. As soon as we have more information we will share it with park visitors."

Anyone who comes across five or more dead wild birds should call Defra’s helpline on 08459 335577.